The measurement of the transmission response of devices in a communications channel is essential for accurate systems modeling. Both the amplitude and phase responses are needed to assess the extent of signal distortion. The most common tool for characterizing non-frequency translating devices is the vector network analyzer (VNA). Due to the VNA design and error correction capabilities, the VNA is fast and accurate. Frequency translating devices (FTDs), such as mixers, are more difficult to characterize due to the frequency offset between input and output, and cannot be measured by a VNA alone. In a typical communication channel, FTDs are often operated as single sideband (SSB) mixers in frequency converters. FTDs are also often used as double sideband (DSB) mixers in modulators and demodulators. For example, in a bi-phase shift-keying modulator, a DSB mixer is often used to convert up a baseband (BB) digital signal. VNAs have disadvantageously not been used to measure the transmission response of FTDS, such as SSB and DSB mixers.
The most common FTD measurement method uses a reference test mixer to obtain the amplitude and phase match between FTDs. A device under test (DUT) FTD is compared to a reference FTD, for example, comparing the difference of the measured response when both the DUT and reference device is an up converter FTD. This reference method is limited in that it only provides the absolute difference between FTDs over a specified frequency range. An extension of the reference method is a known gold standard method. In the known standard method, the transmission response of an FTD can be estimated relative to a known gold standard. By knowing the response of the gold standard FTD, and by measuring the difference in response between the gold standard FTD and the DUT FTD, the DUT FTD response can be calculated. The disadvantage to the known standard method is that the response measurement accuracy is limited to how accurate the known standard has been characterized. Scalar network analyzers can be configured to accurately obtain the conversion loss, that is, the amplitude response, of FTDs as a response measurement. However, this scalar network analyzer method does not completely characterize an FTD because phase information is not included. Another method uses a microwave transition analyzer and an AM or FM envelope delay to characterize SSB FTDs to up to, for example, forty GHz, without the need for a standard reference nor test mixers. As a result, this microwave transition analyzer method has the additional capability of characterizing FTDs with inaccessible internal local oscillators (LOs). The microwave transition analyzer method disadvantageously cannot characterize DSB FTDs and exhibits lower measurement speed and accuracy for SSB FTDs. The transmission response measurement of DSB FTDs is not known to have been performed.
A three pair method has been used to determine the response of antennas. The three pair method measures three antennas in respective paired configurations. The result is a set of measurements from which the response of any one of the antennas can be determined. The three pair method has become standard practice for the gain calibration of antennas wherein the reciprocity property of all three antennas is required. The three pair method has been applied to the measurement of SSB FTDs but has produced inaccurate results. In general, FTDs will not operate as reciprocal devices and thus invalid results are achieved with a direct application of the three pair method. These and other disadvantages are solved or reduced using the invention.